1. Field of the Invention
The present invention relates to a flexible boot for a constant velocity universal joint (CVJ) for use in a driving shaft or the like of an automobile, and particularly, to a flexible boot for CVJ for use in a driving shaft or the like for a rear axle having a small operating angle in an automobile.
2. Description of the Related Art
For a conventional flexible boot for CVJ used in a driving shaft or the like for a rear axle (which will be referred to as a flexible boot for a rear axle hereinafter), a flexible boot for CVJ used in a driving shaft or the like for a front axle (which will be referred to as a flexible boot for a front axle hereinafter) is appropriated in many cases.
The flexible boot for the front axle is constructed, as a common configuration, of a smaller-diameter mounting portion adapted to be supported on the shaft, a larger-diameter mounting portion coaxially disposed at a distance from the smaller-diameter mounting portion and having a diameter larger than that of the smaller-diameter mounting portion, and a bellows portion of a substantially triangular truncated conical shape which integrally connects the smaller-diameter mounting portion and the larger-diameter mounting portion to each other. The bellows portion includes a plurality of crests and a plurality of valleys alternately connected to one another, and a straight portion is formed between the bellows portion and the smaller-diameter mounting portion and has a length 0.1 to 16 times a distance from the center of the smaller-diameter mounting portion to the center of the larger-diameter mounting portion (for example, see JP-A-2002-295509).
In the flexible boot for the front axle, it is conventionally necessary for the function of the flexible boot to increase the development length of the bellows (the total distance of an outer periphery of the bellows portion) so as to withstand an operating angle of up to 50 degree. For this reason, the number of the crests and the valleys of the bellows portion is required to be 5 to 6, resulting in an increase in weight of the flexible boot.
On the contrast, in the flexible boot used for the rear axle, the maximum operating angle is on the order of 15 degree, and the required performance is low, as compared with the flexible boot for the front axle.
Therefore, the conventional flexible boot suffers from the following problem: When the flexible boot for the front axle is appropriated intact for the flexible boot for the rear axle, there is no deficiency in respect of the quality and the function, but the weight of the flexible boot is increased, which is unsuitable for a reduction in weight of a vehicle, and which brings about an increase in cost.